Syringe

ABSTRACT

An improved syringe for dispensing accurately measured quantities of fluid specimens. It comprises a unique plunger and plunger guide assembly, adapted for engagement with a pair of ferrules fitted upon a syringe barrel, in addition to the usual combination of a barrel and a hollow or tubular needle mounted on the forward end of the barrel such that the axial opening of the barrel and the needle opening are communicated to provide a continuous bore. A pair of ferrules, each provided with a plurality of openings (preferably two) of equal number, are fitted upon the barrel, one to the rear and one to the front of the barrel. The openings of the ferrules are aligned. The forward ferrule is adjustably movable upon the barrel, while the other is fixed. The rearward ferrule is provided with openings which subtend a larger arc distance than those of the forward ferrule. The plunger guide, a sub-component of a plunger assembly, comprising a plunger and a plunger guide, is mounted upon the barrel for slidable engagement therewith, via projections corresponding to the number of openings within the ferrules, which are extended through the openings of the rearward ferrule. In one position the terminal ends of members located on the plunger guide will impinge on the front ferrule, this corresponding with a pre-selected setting of the volume of a fluid specimen to be delivered, and in another position the entire plunger assembly can be partially rotated upon the barrel and within the openings of the rear ferrule so that the members of the plunger guide can pass through the openings of the forward ferrule such that the plunger can then be pushed forward to deliver the fluid specimen through the needle.

llnited States Patent 11 1 Harris, Sr. et al.

[ SYRHIGE [76] lnventors: 1151.6 J. Harris, Sr., 9880 S. LiveroaksDrive; Rano J. Harris, .112, 1945 Carolyn Sue Drive, both of BatonRouge, La. 70815 22 Filed: June 22, 1971 211 Appl. No.: 155,570

[52] U.S. Cl. ..222/31, 128/218 C, 128/234,

222/386 [51] Int. Cl. ..B67d 5/22 [58] Field of Search ..222/3l, 326,327,

218C, 218 D, 218 P, 218 PA, 219, 220, 234,

An improved syringe for dispensing accurately measured quantities offluid specimens. It comprises a unique plunger and plungerguideassembly, adapted 14 1 May 1,1973

for engagement with a pair of ferrules fitted upon a syringe barrel, inaddition to the usual combination of a barrel and a hollow or tubularneedle mounted on the forward end of the barrel such that the axialopening of the barrel and the needle opening arecommunicated to providea continuous bore. A pair of ferrules, each provided with a plurality ofopenings (preferably two) of equal number, are fitted upon the barrel,one to the rear and one to the front of the barrel. The openings of theferrules are aligned. The forward ferrule is adjustably movable upon thebarrel, while the other is fixed. The rearward ferrule is provided withopenings which subtend a larger arc distance than those of the forwardferrule. The plunger guide, a sub-component of a plunger assembly,comprising a plunger and a plunger guide, is mounted upon the barrel forslidable engagement therewith, via projections corresponding to thenumber of openings within the ferrules, which are extended through theopenings of the rearward ferrule. In one position the terminal ends ofmembers located on the plunger guide will impinge on the front ferrule,this corresponding with a pre-selected setting of the volume of a fluidspecimen to be delivered, and in another position the entire plungerassembly can be partially rotated upon the barrel and within theopenings of the rear ferrule so that the members of the plunger guidecan pass through the openings of the forward ferrule such that theplunger can then be pushed forward to deliver the fluid specimen throughthe needle.

12 Claims, 7 Drawing Figures PATENTEB MAY 1 I975 IINVENTORS RANO J.HARRIS, SR. RANO'J. HARRIS, JR.

ig QMGQD. C1 TTORNEY SYRINGE Syringes have gained wide acceptance by theindustry, and by the scientific community, generally, for use indispensing infinitesimally small, accurately measured fluid specimens,e.g., to modern analytical instruments such as mass spectrometers andgas chromatographs. Such syringes embody apparatus comprising a tubularbody or barrel, on the forward end of which is fitted a hollow ortubular needle and, at the opposite end, a slidable plunger whichtravels within the barrel. In the most accurate of existing syringes,the measured fluid is dispensed by the positive action of a very smalldiameter wire plunger which travels the length of the barrel. Syringesof this character are capable of dispensing very small fluid specimensmeasured on the order of very small fractions of a microliter.

The syringe embodied by the present invention provides furtherimprovements over prior art devices.

Among the objects of this invention are:

To provide a new and improved syringe capable of more rapidly measuringout infinitesimally small, accurately measured fluid specimens,particularly fractional incrementsof liquid representative of the totalvolumetric capacity of a given syringe.

To provide a syringe of simple structure which can be repetitivelyfilled to a pre-selected setting, with precision and accuracy, and thefluid specimen then injected with similar precision and accuracy Toprovide a syringe particularly adapted for the precise measurement ofliquids without significant error introduced by paralax, as oftenoccasioned by inaccurate observations of the location of a very fineplunger tip in relation to scribed indicia marks.

To provide a syringe having a plunger which can be adjusted to thelength of the bore, and to the zero marking, by very simple manualmanipulations.

To provide a more durable syringe of simple structure, particularly onewherein there are no complicated alignments to be made between theplunger tip and the end of the needle, whereat it enters into thebarrel, such as can cause excessive wear and create maintenancedifficulties.

These and other objects are achieved in accordance with the presentinvention which embodies improvements in syringes comprising the usualcombination of a tubular member or barrel within the forward end ofwhich is provided a hollow or tubular needle, and within the oppositeend of which is fitted. a wire plunger, reciprocably mounted within thebore of the barrel. In the improved combination, a pair of ferrules,each provided with a plurality of openings between the respective memberand the external surface of the wall which forms the barrel, are locatedupon the barrel, one to the rear and one to the front of the barrel. Innormal operative position the front ferrule is adjustable, and thetrailing edge thereof can be set to correspond to a desired scalesetting. The openings of both the front and rearward ferrules arealigned one upon the other, and the openings of the rearward ferrule,which in normal operation is located in a fixed position off the scaleof the barrel, is slightly off-set or subtends a wider arc length thanthose of the front ferrule. The plunger assembly, which includes both aplunger guide and plunger, is of special design and is adapted to workin combination with the said pair of ferrules located on the barrel.

The plunger guide is comprised of a member upon which is mounted aplurality of projecting fingers or branches alternately disposed incircular pattern, the number corresponding with the number of openingswithin the ferrules, and the inner faces of which are curved tocorrespond substantially with the curvature of the barrel upon whichthey are fitted for slidable engagement. In a preferred design theplunger guide is formed from a tubular sleeve, the wall of which isdeeply notched from its forward end by a pair of op positely disposednotches to provide a pair of branches which project from a tubular wallsegment. The tubular wall segment is threadably adapted to receive aplunger. A preferred feature of the invention is that it provides a zeroplunger adjustment. A small tubular member, or adjustable stop, can alsobe mounted on the plunger forward of the said threaded plunger portionand within the tubular wall segment to provide a means for adjustment ofthe length of the wire plunger which extends into the bore of thebarrel. In position,

the projecting surfaces of the plunger guide are extended through theopenings of the rearward ferrule and span the barrel, the wire portionof the plunger is mounted within the bore of the barrel, and the wholeof the plunger assembly is reciprocable, and rotatable to a limitedextent within the openings of the rearward ferrule. In one position theterminal ends of the projecting members of the plunger guide willcontact or impinge upon the front ferrule, the trailing edge of thismember being pre-set to provide a measured volume of a fluid specimen tobe delivered through the needle and, in another position, the entireplunger assembly can be partially rotated upon the barrel and within theopenings of the rearward ferrule so that the projecting members of theplunger guide can enter the openings of the front ferrule and pushedforward to deliver the indicated amount of fluid specimen through theneedle.

The invention, and its principle of operation, will be more fullyunderstood by reference to the following detailed description of aspecific embodiment, and to the attached drawings to which reference ismade in the description. In the description, similar numbers are used torepresent similar parts or components, and subscripts are used wherethere are a plurality of similar parts or components.

In the drawings:

FIG. 1 is a perspective view, depicted in exploded fashion, of apreferred type of syringe embodying the present invention;

FIG. 2 is a perspective view of the syringe of the preceding figure inassembled form;

FIGS. 3-5, by reference to a progressive series of fragmentary views ofthe forward end of the assembled syringe, depict a sequence describinginjection of a specimen;

FIG. 6 is a section taken on the line 6-6 of FIG. 2; and

FIG. 7 is a section taken on line 7-7 of FIG. 2.

Referring to the drawings, particularly to FIG. 1, there is shown asyringe indicated generally by the numeral 10. The syringe 10 includesgenerally a hollow barrel or tubular body 11, provided by an enclosingwall which defines a central axial opening or bore. In its preferredform the barrel 1 1 is formed of glass or transparent plastic, mostpreferably the former, and outwardly scribed with indicia marksrepresentative of the volume of the bore. A cannula or tubular needle 12is tightly mounted, and sealed within the forward end of the barrel 11,the bore of the needle being aligned upon the axial opening or borethrough the center of the barrel 11. A plunger assembly, comprisedgenerally of a plunger guide 21 and plunger 32, is mounted at therearward end of the barrel 11, the plunger 32 being reciprocably movablethrough the bore of the barrel.

The plunger guide 21 can be constructed as a unitary member, describedgenerally as a cylindrical member with deeply slotted sides 21 ,22which, in effect, provide a tubular segment and a pair of alternatelydisposed guide members 23 ,23 In all embodiments a plurality of guidemembers 23 are provided, the inside curvature of a guide membersubstantially corresponding with the outside curvature of the wall whichforms the barrel 11 so that the plunger guide 21 can grasp and freelyslide upon the barrel 11 as the plunger 32 is reciprocated within thebore of the barrel 11. The closed end or tubular segment of the plungerguide 21 is internally threaded, and the threads 24 adapted forthreadable engagement with the externally threaded shank portion 31 ofplunger 32 so that both the plunger guide 21 and plunger 32 are held infixed relationship, one with respect to the other, when the syringe isassembled. The plunger guide 21 can be constructed of essentially anyrigid or semi-rigid material, but preferably is constructed of metalsuch as aluminum, ferrous metals or their alloys, and the like.

The plunger 32 is constructed of wire of very thin cross-sectionaldiameter, and the forward end or tip 36 thereof can be capped by ahighly preferred type of stress formed seal, e.g., a Teflon seal, suchas described in U.S. Pat. No. 3,577,850 which issued May ll, 1971,herewith incorporated by way of reference. A thumb button 33 is locatedupon the opposite end of the plunger 32, the thumb button 33 beingadjoined to the plunger wire via the threaded projections or shankportions 31,34. The threaded shank 31 mates with internal threads 24 ofthe plunger guide 21 so that the plunger guide 21 and plunger 32 areheld in fixed relationship, one member with respect to the other, whenthe syringe is assembled. The internally threaded cylindrical or tubularmember 35 in combination with the threaded shank portion 34 of theplunger 32 provides a means of adjustment by virtue of which the tip 36of the plunger can be conveniently set at the zero filling mark, thispoint generally being just barely short of the terminal end of theneedle 12. This is accomplished by setting the distance within which theplunger can be extended into the bore of the barrel 1]. The tubularmember 35 is thus a plunger stop which is adapted to fit tightly inposition near the rearward end of plunger 32, but yet sufficiently looseas to be movable between adjustments. A tight fit wherein the diameterof the wire plunger exceeds the internal diameter by about 0.001 inch isgenerally adequate. Preferably, the tubular member 35 is adapted forthreadable engagement with the external threads of smaller diametershank portion 34 of plunger 32, such that rotation of the tubular member35 relative to the shank 34 will produce movement of the tubular member35 in one of the two possible directions along the shank. If the tubularmember 35 is thus threaded such that when rotated it will move towardthe tip 36 of plunger 32, the length of the wire portion of the plungerthat can be extended through the bore of barrel 11 will be shortened.Conversely, if the tubular member 35 is rotated such that it is moved inthe opposite direction, the effective length of the wire portion of theplunger will be lengthened. Setting the tip 36 of the plunger 32 justshort of contact with the terminal end of the needle 12, where it entersinto the bore of barrel 11, prevents damage to the plunger tip andprevents packing of infinitesimally small solid contaminants into theneedle opening. I

In assembled position, as best shown by reference to FIG. 2, the pair ofplunger guide members 23 ,23 are passed through openings 14 ,14 of thebushing or ferrule 13 which is fixed upon the rearward end of barrel 11,the inside faces thereof being fitted to the curvature of the outsidewall of the said barrel for reciprocable slidable movement thereon. Theferrule 13 is positioned and held tightly in place upon barrel 11 by athreaded bolt or screw 15 which is fitted through a threaded tap forphysical contact of the end thereof with the side wall of barrel 1 l.The ferrule 16, also provided with a pair of openings 17 ,17 throughwhich the plunger guide members 23 ,23 can be passed, is similarlypositioned and held tightly in place upon the forward end of barrel 11.The arc subtended by the openings 17 ,17 is somewhat less than thatsubtended by the the openings 14 ,14 of fixed ferrule 13. The positionof the forward ferrule 16 is normally adjusted, during the variousoperations, with its trailing edge upon the precise volume of specimen,as represented by the indicia mark with which it corresponds, which isto be delivered through the dispensing end of the needle 12.

In describing a specific operation, it is supposed, for example, thatthe tip 36 of plunger 32 has been set to flush with the zero mark, thata screw 18 of forward ferrule 16 have been loosened and the ferrule 16moved such that its trailing edge is aligned upon the indicia markrepresenting 2 microliters, this setting corresponding to a bore volumebetween the readings zero and two" or two microliters. The bolt or screw18 is then tightened into place so that the end and at thereof contactsthe outside wall of barrel 11 and prevents relative movement betweenbarrel 11 and ferrule 16. The amount of the fluid specimen desired to beinjected then is 2 microliters and somewhat more than this volume of aspecimen has been withdrawn from a source (not shown), and the settingof the instrument then is as described by reference to FIG. 2. Referringto FIG. 3, the plunger 32 is pushed forward until the terminal ends ofthe plunger guide members 23 ,23 come into contact with the trailingedge of forward ferrule 16. Liquid specimen in excess of two microlitersis thus rejected, any residual specimen is wiped from the dispensing endof the needle 12, and the syringe is ready to inject the 2 microlitersof specimen into, e.g., the septum of a modern analytical instrument,such as a mass spectrometer or gas chromatograph for chemical analysis.

To accomplish injection of the two microliter specimen, the plungerassembly is rotated counterclockwise so that the terminal ends ofplunger guide members 23 ,23 are aligned upon the openings 17 ,17 of theforward ferrule 16 as shown by reference to FIG. 4. It is to be notedthat thearc lengths of openings 14 ,14 of ferrule 13 are sufficientlygreat as to permit this slight rotation of the plunger assembly uponbarrel ii 1. For delivery or injection of the accurately measured 2microliter specimen, the plunger 32 is then pushed forward such that thespecimen is expelled by the positive action of the plunger as shown byreference to FIG. 5.

The relative sizes, and locations, of openings 14 ,14 of fixed ferrule13 and openings 17 ,17 of movable ferrule 16 and the angles subtended bythearcuate lengths of the respective openings are readily observed byreference to FIGS. 6 and 7. It is seen, by comparisons of these figures,that sufficient space is provided within the 'left side of openings 14,14 that the plunger assembly can be readily shifted bycounter-clockwise rotation and, in so doing, that the pair of plungerguide members 23,,23 can be aligned upon openings 17 ,17 so that theycan be passed therethrough when the plunger is moved forward.

A prime purpose of the plunger guide members 23 ,23 is to maintainalignment of, and to guide the thin wire plunger 32 through, thecontinuous bore of the barrel 1 1. An important feature of the design ofthis syringe, however, including particularly the design of the plungerguide assembly, is that paralax can be virtually eliminated from syringereadings. In preferred embodiments, the plunger guide members 23 ,23 areof equal length and the terminal ends of plunger guide members 23 ,23are precisely aligned, one with the other, and upon the extreme terminalforward end of tip 36 of the plunger 32. By precisely aligning thesethree reference points, an exact reading can be taken at any scalelocation on the barrel 11. It is preferred also that at the zero markall three of these reference points are precisely aligned upon zero.

It is apparent that various modifications and changes can be madewithout departing the spirit and scope of the present invention. Theapparatus is constructed of materials substantially inert ornon-reactive to the chemical or corrosive action of the fluid specimensto be measured and dispensed. The barrel is normally constructed ofglass, but can be constructed of a plastic or plastic-like material. Theforward seal located on the plunger tip and the tubular member used toadjust the limits of the plunger stroke are normally constructed ofplastic, and the rest of the syringe of various metals.

The tubular member and the seal are preferably formed of a rigid orsemi-rigid, resilient form of plastic or plastic-like material. Theself-lubricated plastics are especially preferred in this capacity, andcan also be applied as a laminate or protective film. Thepolyfluorinated ethylene polymers, notable among which ispolytetrafluoroethylene (Teflon), are particularly outstanding.Conventional resilient or elastic-like materials, such as natural orsynthetic rubbers, can also be employed.

The plunger assembly and the needle of the syringe are preferablyconstructed of metals, e.g., ferrous metals such as iron, ironalloysQsteel, stainless steels, and the like; or such metals asaluminum, magnesium, brass, copper, bronze, chrome, alloys of these andother metals, and the like.

It is apparent that various changes, such as in the absolute or relativedimensions of the parts, materials used, and the like, as well as thesuggested mode of withdrawing or delivering fluids, can be made withoutdeparting the spirit and scope of the invention, as will be apparent tothose skilled in this art.

Having described the invention, what is claimed is:

1. In a syringe for dispensing small, accurately measured quantities offluid specimens, the combination comprising a barrel formed by anenclosing wall defining an axial opening,

a hollow needle mounted at the forward end of the barrel, the openingthrough the said needle communicating with the axial opening through thebarrel,

a pair of ferrules, each containing a central opening forming a ringthrough which the barrel is slidably fitted, a plurality of openingswithin the ring portion of each of the ferrules, a first ferrule beinglocated toward the rear of the barrel while a second ferrule, located infront of the first ferrule, can be adjustably located in differentpositions along the length of the barrel, the arc lengths of theopenings within the ring portion of the first ferrule being greater thanthat of the openings within the ring portion of the second ferrule uponwhich they are aligned,

a plunger assembly including a plunger guide and plunger, said plungerguide including a tubular member, the

wall of which is cut away from the forward end by a plurality of deepslots to provide a tubular segment and a plurality of alternatelydisposed projecting plunger guide members, corresponding in number withthe number of openings within the ring portions of the said ferrules,the inside faces of each of which are curved to correspond substantiallywith the outside curvature of the wall which forms the barrel so thatthese members can grasp and freely slide upon the external. wall of thebarrel, said plunger including a shank portion which is operativelyengaged to the tubular segment of the plunger guide, whereby, inassembled position, the plunger guide members are located within andpass through the openings of the first ferrule, the plunger ismaintained in alignment with and reciprocably movable within the axialopening of the barrel, and wherein, in one position, the terminal endsof the plunger guide members will impinge upon the second ferrule, thiscorrespond ing to a preselected setting of a volume of a fluid specimento be delivered through the needle and, in another position, the entireplunger assembly can be partially rotated upon the barrel and within theopenings within the ring portion of the first ferrule so that theterminal ends of the plunger guide member can pass through the openingswithin the ring portion of the said second ferrule and the plunger thenpushed forward to deliver the said accurately measured volume of thefluid specimen.

2. The apparatus of claim 1 wherein two openings are contained withineach of the ferrules, and two oppositely disposed plunger guide membersare contained within the plunger guide.

3. The apparatus of claim I wherein the tubular segment of the plungerguide is internally threaded and the plunger is provided with anexternally threaded shank, such that the tubular segment and plunger canbe threadably engaged, one member to the other.

4. The apparatus of claim 1 wherein the tubular segment of the plungerguide is internally threaded, the plunger is provided with an externalshank of two different diameters, the smaller diameter shank beingcontiguous to the terminal end of the plunger and adapted to receive atubular member of smaller external diameter than that of the openingwithin the tubular segment of the plunger guide while the largerdiameter shank is externally threaded and thereby adapted for threadableengagement with the internally threaded tubular segment of the plungerguide, and wherein the said tubular member for location on the smallerdiameter shank portion of the plunger is movable thereon so that thelength of the plunger can be adjusted.

5. The apparatus of claim 4 wherein a thumb button is attached upon thelarger diameter shank portion of the plunger.

6. The apparatus of claim 4 wherein the smaller diameter shank portionof the plunger is externally threaded and the tubular member adapted formovement thereon is internally threaded for threadable engagementtherewith.

7. The apparatus of claim 6 wherein the tubular member consistsessentially of Teflon.

8. The apparatus of claim 1 wherein the barrel is comprised of glass,and indicia marks are scribed thereon.

9. The apparatus of claim 1 wherein the ferrules are comprised ofTeflon, adjustably secured in place upon the wall of the barrel bybolts.

10. The apparatus of claim 1 wherein the forward tip of the plunger iscapped with a seal.

11. In a syringe for dispensing small, accurately measured quantities offluid specimens, the combination comprising a barrel formed by anenclosing wall defining an axial opening,

a hollow needle mounted at the forward end of the barrel, the openingthrough the said needle communicating with the axial opening through thebarrel,

a pair of ferrules, each containing a central opening forming a ringthrough which the barrel is slidably fitted, a pair of alternatelydisposed slot-like openings within the ring portion of each of theferrules, a first ferrule being located toward the rear of the barrelwhile a second ferruleflocated in front of the first ferrule and on theforward end of the barrel, can be adjustably moved and located indifferent positions along the length of the barrel, the arc lengths ofthe pair of slot-like openings within the ring portion of the firstferrule being greater than that of the pair of slot-like openings withinthe ring portion of the second ferrule upon which they are aligned, aplunger assembly including a plunger guide and plunger, said plungerguide including a tubular member, the wall of which is cut away from theforward end by a pair of alternately disposed deep slots to provide atubular segment, the inside surface of which is threaded, and a pair ofalternately disposed pro ecting plunger guide members, the

width of each of which is lesser than that of either of the slot-likeopenings within the ring portion of both the first and second ferrule,and the inside faces of each of the plunger guide members are curved tocorrespond substantially with the outside curvature of the wall whichforms the barrel so that these members can grasp and freely slide uponthe external wall of the barrel, said plunger including a shank portion,a small diameter externally threaded forward portion, and a largerdiameter externally threaded portion which is threadably engaged to thesaid tubular segment of the plunger guide, an internally threadedtubular member of diameter greater than that of the axial openingthrough the barrel located on the externally threaded smaller diametershank portion of the plunger, and axially movable thereon, so that thelength of the plunger which can be extended into the axial opening ofthe barrel can be adjusted, whereby, in assembled position, the plungerguide members are located within and pass through the openings of thefirst ferrule, the plunger is maintained in alignment with andreciprocably movable within the axial opening of the barrel, andwherein, in one position, the terminal ends of the plunger guide memberswill impinge upon the ring portion of the second ferrule, thiscorresponding to a preselected setting of a volume of a fluid specimento be delivered through the needle and, in another position, the entireplunger assembly can be partially rotated upon the barrel and within theopenings within the ring portion of the first ferrule so that theterminal ends of the plunger guide member can pass through the openingswithin the ring portion of the said second ferrule and the plunger thenpushed forward to deliver the said accurately measured volume of thefluid specimen. 12. The apparatus of claim 11 wherein the internallythreaded member is constructed of Teflon, the barrel is comprised ofglass with indicia marks scribed thereon, the ferrules are constructedof Teflon, adjustably secured in place upon the wall of the barrel bybolts, and the forward tip of the plunger is capped with a Teflon seal.

1. In a syringe for dispensing small, accurately measured quantities offluid specimens, the combination comprising a barrel formed by Anenclosing wall defining an axial opening, a hollow needle mounted at theforward end of the barrel, the opening through the said needlecommunicating with the axial opening through the barrel, a pair offerrules, each containing a central opening forming a ring through whichthe barrel is slidably fitted, a plurality of openings within the ringportion of each of the ferrules, a first ferrule being located towardthe rear of the barrel while a second ferrule, located in front of thefirst ferrule, can be adjustably located in different positions alongthe length of the barrel, the arc lengths of the openings within thering portion of the first ferrule being greater than that of theopenings within the ring portion of the second ferrule upon which theyare aligned, a plunger assembly including a plunger guide and plunger,said plunger guide including a tubular member, the wall of which is cutaway from the forward end by a plurality of deep slots to provide atubular segment and a plurality of alternately disposed projectingplunger guide members, corresponding in number with the number ofopenings within the ring portions of the said ferrules, the inside facesof each of which are curved to correspond substantially with the outsidecurvature of the wall which forms the barrel so that these members cangrasp and freely slide upon the external wall of the barrel, saidplunger including a shank portion which is operatively engaged to thetubular segment of the plunger guide, whereby, in assembled position,the plunger guide members are located within and pass through theopenings of the first ferrule, the plunger is maintained in alignmentwith and reciprocably movable within the axial opening of the barrel,and wherein, in one position, the terminal ends of the plunger guidemembers will impinge upon the second ferrule, this corresponding to apreselected setting of a volume of a fluid specimen to be deliveredthrough the needle and, in another position, the entire plunger assemblycan be partially rotated upon the barrel and within the openings withinthe ring portion of the first ferrule so that the terminal ends of theplunger guide member can pass through the openings within the ringportion of the said second ferrule and the plunger then pushed forwardto deliver the said accurately measured volume of the fluid specimen. 2.The apparatus of claim 1 wherein two openings are contained within eachof the ferrules, and two oppositely disposed plunger guide members arecontained within the plunger guide.
 3. The apparatus of claim 1 whereinthe tubular segment of the plunger guide is internally threaded and theplunger is provided with an externally threaded shank, such that thetubular segment and plunger can be threadably engaged, one member to theother.
 4. The apparatus of claim 1 wherein the tubular segment of theplunger guide is internally threaded, the plunger is provided with anexternal shank of two different diameters, the smaller diameter shankbeing contiguous to the terminal end of the plunger and adapted toreceive a tubular member of smaller external diameter than that of theopening within the tubular segment of the plunger guide while the largerdiameter shank is externally threaded and thereby adapted for threadableengagement with the internally threaded tubular segment of the plungerguide, and wherein the said tubular member for location on the smallerdiameter shank portion of the plunger is movable thereon so that thelength of the plunger can be adjusted.
 5. The apparatus of claim 4wherein a thumb button is attached upon the larger diameter shankportion of the plunger.
 6. The apparatus of claim 4 wherein the smallerdiameter shank portion of the plunger is externally threaded and thetubular member adapted for movement thereon is internally threaded forthreadable engagement therewith.
 7. The apparatus of claim 6 wherein thetubular member consists essentially of Teflon.
 8. The apparatus of claim1 wheRein the barrel is comprised of glass, and indicia marks arescribed thereon.
 9. The apparatus of claim 1 wherein the ferrules arecomprised of Teflon, adjustably secured in place upon the wall of thebarrel by bolts.
 10. The apparatus of claim 1 wherein the forward tip ofthe plunger is capped with a seal.
 11. In a syringe for dispensingsmall, accurately measured quantities of fluid specimens, thecombination comprising a barrel formed by an enclosing wall defining anaxial opening, a hollow needle mounted at the forward end of the barrel,the opening through the said needle communicating with the axial openingthrough the barrel, a pair of ferrules, each containing a centralopening forming a ring through which the barrel is slidably fitted, apair of alternately disposed slot-like openings within the ring portionof each of the ferrules, a first ferrule being located toward the rearof the barrel while a second ferrule, located in front of the firstferrule and on the forward end of the barrel, can be adjustably movedand located in different positions along the length of the barrel, thearc lengths of the pair of slot-like openings within the ring portion ofthe first ferrule being greater than that of the pair of slot-likeopenings within the ring portion of the second ferrule upon which theyare aligned, a plunger assembly including a plunger guide and plunger,said plunger guide including a tubular member, the wall of which is cutaway from the forward end by a pair of alternately disposed deep slotsto provide a tubular segment, the inside surface of which is threaded,and a pair of alternately disposed projecting plunger guide members, thewidth of each of which is lesser than that of either of the slot-likeopenings within the ring portion of both the first and second ferrule,and the inside faces of each of the plunger guide members are curved tocorrespond substantially with the outside curvature of the wall whichforms the barrel so that these members can grasp and freely slide uponthe external wall of the barrel, said plunger including a shank portion,a small diameter externally threaded forward portion, and a largerdiameter externally threaded portion which is threadably engaged to thesaid tubular segment of the plunger guide, an internally threadedtubular member of diameter greater than that of the axial openingthrough the barrel located on the externally threaded smaller diametershank portion of the plunger, and axially movable thereon, so that thelength of the plunger which can be extended into the axial opening ofthe barrel can be adjusted, whereby, in assembled position, the plungerguide members are located within and pass through the openings of thefirst ferrule, the plunger is maintained in alignment with andreciprocably movable within the axial opening of the barrel, andwherein, in one position, the terminal ends of the plunger guide memberswill impinge upon the ring portion of the second ferrule, thiscorresponding to a pre-selected setting of a volume of a fluid specimento be delivered through the needle and, in another position, the entireplunger assembly can be partially rotated upon the barrel and within theopenings within the ring portion of the first ferrule so that theterminal ends of the plunger guide member can pass through the openingswithin the ring portion of the said second ferrule and the plunger thenpushed forward to deliver the said accurately measured volume of thefluid specimen.
 12. The apparatus of claim 11 wherein the internallythreaded member is constructed of Teflon, the barrel is comprised ofglass with indicia marks scribed thereon, the ferrules are constructedof Teflon, adjustably secured in place upon the wall of the barrel bybolts, and the forward tip of the plunger is capped with a Teflon seal.